-: Network performance issues. 2 2
In this video, we're going to discuss 3 3
how to troubleshoot network performance issues 4 4
that you may experience out in the field. 5 5
Now the five most common causes 6 6
of network performance issues 7 7
are high CPU usage in a network device, 8 8
high bandwidth usage in a network, 9 9
poor physical connectivity, 10 10
malfunctioning of your network or DNS problems. 11 11
First, it's important to realize that every network device 12 12
such as your routers, switches and firewalls 13 13
are at their core, a computer. 14 14
That includes a CPU or central processing unit. 15 15
If that device begins to experience 16 16
a high CPU utilization rate, 17 17
that device is going to start slowing down and in turn, 18 18
the network that is being processed for all those packets 19 19
is also going to slow down. 20 20
So whenever a CPU is overutilized, 21 21
the latency, jitter and packet loss will start to increase 22 22
and this can cause the entire network performance 23 23
to deteriorate on you. 24 24
So to solve this issue, you need to either 25 25
upgrade your network devices to more powerful ones 26 26
such as enterprise class routers and firewalls 27 27
or you need to simplify the processing load 28 28
that you're putting on those devices. 29 29
For example, I once saw an enterprise network 30 30
where their border firewall 31 31
was slowing down the entire network. 32 32
Now when we looked at it closer, 33 33
we saw their access list had over 3,000 entries in it. 34 34
That meant that every time a packet was received, 35 35
it was checked against these 3,000 individual entries 36 36
to find its match or to eventually block that packet. 37 37
Now this consumes a lot of processing time 38 38
and leads to high CPU utilization rates. 39 39
Now we conducted an ACO review 40 40
and we were able to simplify their rule set 41 41
down to about 300 rules. 42 42
This drastically reduced the CPU utilization rate they had 43 43
and sped up the network. 44 44
Second, high bandwidth utilization 45 45
is another cause of network performance deterioration. 46 46
Now when bandwidth utilization is high, 47 47
network communications have to wait 48 48
to enter or leave that network. 49 49
This can cause buffers to fill up 50 50
and in the worst cases, packets can be dropped. 51 51
Now when those packets are dropped, 52 52
they're going to be retransmitted if they were sent using TCP. 53 53
And this leads again, 54 54
to even higher bandwidth utilization rates 55 55
because we have retransmissions. 56 56
To solve this issue, 57 57
you can either increase your bandwidth size 58 58
by paying more to your internet service provider 59 59
or you can do a network flow analysis 60 60
and determine what sites and traffic types 61 61
are being used by all of your clients. 62 62
For example, if 90% of your traffic is being wasted 63 63
by people scrolling Facebook each day, 64 64
you may need to change your acceptable use policy 65 65
or reduce or eliminate 66 66
when people are allowed to use Facebook on your network. 67 67
Literally, I had one network where 90% of our traffic 68 68
was either going to or coming from Facebook 69 69
and our end users kept complaining 70 70
because they couldn't do any real work on their job 71 71
because our internet was so slow. 72 72
And this is why conducting a NetFlow analysis 73 73
can really help you understand 74 74
what your users are really doing on your network 75 75
and is it something you want to allow. 76 76
Third, you may have network performance issues 77 77
if you have a poor physical connection. 78 78
To solve this, you're going to need to check your cables 79 79
and test them one by one. 80 80
Now if you suspect it's an issue 81 81
with the internet search provider's portion of the network, 82 82
you need to connect a test client 83 83
directly to the demarcation point 84 84
and test the connection from there. 85 85
If that connection is poor, 86 86
then you know it's your ISP's problem to solve. 87 87
If it isn't, that means it's something in your network 88 88
that's the problem and you need to start testing every cable 89 89
from the from the demarc point 90 90
all the way back to your border router 91 91
and then to your switch and then to your client 92 92
until you find where that broken or damaged cable might be 93 93
that's causing the slowdown in your network connection. 94 94
Remember, a damaged cable may still operate, 95 95
but it's going to cause additional errors 96 96
and these errors require data 97 97
to be retransmitted over and over again 98 98
and this slows down your overall network performance. 99 99
To test your cables, always use a cable tester 100 100
for twisted pair connections 101 101
or a fiber light meter for fiber optic connections. 102 102
Fourth, we have malfunctioning of our network. 103 103
Now if you have misconfigurations of your devices 104 104
or hardware failures, 105 105
your network performance is obviously going to suffer. 106 106
Sometimes this can even be caused 107 107
by using old or outdated network operating systems. 108 108
Again, this is an area 109 109
where your seven step troubleshooting method 110 110
is going to help you identify the exact location 111 111
of the device that's having these issues 112 112
and then you can focus on whether it's a configuration issue 113 113
or a hardware failure issue 114 114
that's causing those network performance issues. 115 115
Finally, fifth, we have DNS problems in our network. 116 116
Now we already talked specifically about DNS issues 117 117
in a separate lesson, 118 118
but DNS issues are a serious cause 119 119
of a lot of our network performance issues. 120 120
Remember, if you have a high DNS latency, 121 121
this is going to slow down the overall user experience 122 122
because when that user requests a website, 123 123
they first have to go and resolve that domain name 124 124
all the way out to that DNS server 125 125
and get the IP address over DNS.